This application relates to magnetic disc drives and more particularly to a disc drive assembly having a multilayer acoustic damper to improve disc drive acoustics.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on an information storage disc. Modern disc drives comprise one or more rigid information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads in an arc across the surface of the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The recording transducer, e.g. a magneto resistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to a host computing system.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Typically, such radial actuators employ a voice coil motor to position the heads with respect to the disc surfaces. The actuator voice coil motor includes a coil mounted on the side of the actuator body opposite the head arms so as to be immersed in the magnetic field of a magnetic circuit comprising one or more permanent magnets and magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
A major concern in the disc drive field is acoustic noise generated during disc drive operation. Such noise is aggravating to the user and its minimization is one of the disc drive designer""s goals. Vibrations caused by rotation of the spindle motor, air turbulence around the outer diameter of rotating discs, and other normal operation force transmitting events lead to acoustic emissions from a disc drive. Typically, the disc drive housing, i.e., base plate and top cover, exhibit negligible properties for damping structural vibrations. In fact, the top cover often acts like a vibrating speaker to amplify acoustic emissions, thus exacerbating the acoustic emission problem. An acoustic damper is often added to the housing to minimize acoustic emissions from the disc drive. Dampers can be integrated into the housing walls or can be added as a separate piece or unit to a housing surface.
Acoustic dampers typically are made from a thin layer of metal such as steel adhered to a surface of the housing by a visco-damping layer of adhesive. The damper reduces acoustic emissions from the housing by two mechanisms: (1) the additional mass of the damper adhered to the housing serves to shift the natural frequency of the housing and thus reduce the overall displacements induced by acoustic sources; and (2) the visco-damping adhesive absorbs acoustic energy. The combined effect on the disc drive is to reduce the acoustic emissions and provide a quieter and more stress free environment for the user.
A major shortcoming of current disc drive acoustic dampers is their inability to absorb energy over a varied temperature and frequency range. Conventionally, adhesives formulated for room temperature are utilized in acoustic dampers because disc drives are processed and assembled at room temperature and because the temperature within the disc drive often remains in close approximation to room temperature. However, the new generation of 7200 rpm, 10,000 rpm and 12,500 rpm disc drives operates within a normal temperature range of 20xc2x0-55xc2x0 C. The increased operating temperature tends to decrease the tack of the room temperature formulated adhesives as well as to reduce the adhesive""s effectiveness at dampening acoustic emissions. Against this backdrop the present invention has been developed.
The above problems and other problems have been solved in accordance with the present invention by incorporating into the damper a number of visco-damping layers, each formulated to optimally perform in a specific temperature or frequency range.
An acoustic damper in accordance with one embodiment of the present invention is adapted to be adhered to a top cover of a disc drive by a first adhesive layer. The first adhesive layer has a maximal damping efficiency within a first operating condition. The acoustic damper has a first constraining layer on the first adhesive layer. A second adhesive layer is sandwiched between the first constraining layer and a second constraining layer. The second adhesive layer is formulated for maximal damping efficiency within a second operating condition where the first and second operating conditions are different. The first and second operating conditions could be temperature ranges or acoustic frequency ranges.
Another embodiment of the present invention is a top cover for a disc drive having an acoustic damper adhered to either the top surface or the bottom surface of the cover. The acoustic damper is adhered to the top cover with a first adhesive layer. The first adhesive layer has a maximal damping efficiency within a first operating condition such as a specific temperature or frequency range. A first constraining layer covers the first adhesive layer. A second adhesive layer is sandwiched between the first constraining layer and a second constraining layer. The second adhesive layer is formulated for maximal damping efficiency within a second operating condition such as another temperature or frequency range different from the first range. The first and second operating conditions may be temperature ranges or acoustic frequency ranges.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.